The present disclosure relates generally to power generation and stability within a power grid and, more specifically, to systems and methods for non-invasive estimation of damping torque for power generators in the power grid.
Some known power systems analyze system stability based on a static view of the system, which may not consider the electro-mechanical interactions among generators, loads, and control devices. With widespread deployment of renewable generation (e.g., solar and wind generators), controllable loads, energy storage devices, and plug-in hybrid electric vehicles expected, greater integration of cyber infrastructure (e.g., communications, computation, and control), monitoring, and controlling th dynamic performance of the power grid in real-time becomes increasingly important.
When analyzing power systems, power system states (e.g., variables) may be classified into two classes, i.e., static states and dynamic states. Static states include various bus voltage magnitudes and phase angles. These measurements may change slowly over a period of time. However, the variations will be small and short-lived. In some known systems, these static state variables have been estimated using a state estimator (SE) utilizing telemetered data from a supervisory control and data acquisition (SCADA) system. Dynamic states include generator rotor speeds and rotor angles, internal differential variables associated with generators, exciters, power system stabilizers, turbine governors, wind generation systems, and other dynamic components in the system (e.g., motor loads). While both of these classes of states vary continuously over time, the dynamic states are the primary variable class which governs the transient response of the system. In many instances, there may be no direct measurement of these dynamic states available from the grid.
Most modern power systems include a number of electric power generating devices substantially synchronized to each other when in service. Each generator has at least some slight differences in physical configuration and operational performance characteristics and constraints, therefore each generator will deviate slightly from the other connected generators with respect to loading. Since the total load on the power system will vary with time continuously as loads are added and removed, each synchronous generator will react to the changes differently. While equilibrium between the electromagnetic and mechanical torques of the generators is substantially maintained, small perturbations in the loading of the power system will initiate shifts of the balance between power demand and power availability in the power system for short periods of time as the synchronized generators adjust to these changes based on their structural and operational configurations and limitations. The change in electromagnetic torque of each synchronous generator following a perturbation is resolved into two components, i.e., a synchronizing torque component in phase with the rotor angle deviation, and a damping torque component in phase with the angular speed deviation. Lack of sufficient synchronizing torque is associated with non-oscillatory instabilities and lack of damping torque results in low frequency oscillations.
A growing challenge inherent in grid integration of more diverse sources of power generation is that of characterizing individual generators' contributions to higher-level, system-wide objectives such as grid stability. Some known stability analysis tools address damping of oscillations through defining the damping torque associated with each generator. However, damping torque estimations using peripheral measurements, such as through voltage and current samples provided by phasor measurement units (PMU's) have traditionally been purely a conceptual tool, with limited success. Therefore, to perform damping torque evaluations of individual generators, the generators must undergo invasive testing, that is, either the generators must be taken out of service for the duration of the testing and analysis or be subject to artificial disturbances while in service. Such invasive testing, however, does not provide for estimating the damping torque contributions from each generator in real-time across different operating conditions.